Manufacturers of vehicles have made significant investments in improving safety in recent years, that is, much effort has been made to reduce loss due to damage of vehicle and injury of passengers, particularly in preparation for a collision.
For example, collisions of vehicles are largely classified into a high-speed collision above 40 km/h and a low-speed collision below 15 km/h. Car bodies are designed in the focus on reducing injury of human body in high-speed collisions, but in the focus on reducing the amount of deformation of car bodies in low-speed collisions.
In particular, a specific part, a crash box having a rectangular closed cross-sectional space inside is provided between a front bumper and a front side member to minimize deformation of a car body at low-speed collisions. Because crash boxes in the related art had to be designed with low stiffness to effectively absorb striking energy at low-speed collisions, not only they could not have sufficient stiffness for high-speed collisions, but also deformation due to a collision was not localized to the crash boxes and progresses to the front side member.
Further, crash boxes in the related art had to be essentially modified in the designs such as increasing closed cross section, thickness of materials, and length of members to absorb striking energy at high-speed collisions on account of their simplicity in the shapes.
However, since the increase of the closed cross section, thickness, and length for crash boxes in the related art is an important matter that changes the whole external shape of the front of a car body, it does not agree with an intention that is to effectively absorb striking energy at a limited space.